1. Technical Field
The present invention relates to an aqueous pigment dispersion and an aqueous ink composition containing the same.
2. Related Art
As a method of forming a coating film having metallic gloss on a printed matter, a die-stamping using a printing ink in which gold powders or silver powders produced from brass or aluminum fine particles are used as a pigment, or a metal foil, and a thermal transfer method using a metal foil have been used in the related art. However, in these methods, there is a problem in which a fine pattern is not easily formed, or application to a curved surface portion is difficult. In addition, in the die-stamping, there is a problem in which on-demand property is low, a response to a multi-product production is difficult, and it is not possible to print a metal tone image with a gradient.
On the other hand, since a powder coating material containing a metal pigment is a low-pollution coating material in which an organic solvent is not used, a demand for the powder coating material is increasing in various industries. However, in a case of the powder coating material containing the metal pigment, if the metal pigment cannot be arranged in parallel to a substrate of a coating film, there is a disadvantage that a color tone of the coating film becomes dark, and a sufficient metallic feeling is not obtained. To overcome such a disadvantage, for example, JP-A-2003-213157 and JP-A-2006-169393 disclose powders for coating material obtained by coating the surfaces of aluminum particles with a fluorine-based (co)polymer which has fluorine-containing (meth)acrylic acid ester as an essential monomer. In addition, JP-A-2009-215411 discloses powders for coating material obtained by coating the surfaces of aluminum particles with a polymerizable fluorine-based (co)polymer which has fluorine-based polymerizable monomers and polymerizable monomers having phosphate groups as an essential monomer.
In recent years, many application examples to ink jet printing have been seen, and as an application example of these, there is a metallic print, and development of an ink having metallic gloss is in progress. The ink jet method is excellent since it can also be suitably applied to the formation of a fine pattern and recording on the curved surface portion. For example, JP-A-2012-251070 and JP-A-2013-122008 disclose an ultraviolet-ray curable type ink jet composition including metal particles and a polymerizable compound.
On the other hand, from the viewpoint of the global environment, safety to the human body, or the like, development of an aqueous ink composition which does not contain an organic solvent or a polymerizable compound, and can form a metallic gloss image has been desired.
However, when a base metal pigment, in particular, an aluminum pigment is dispersed in water, hydrogen gas is generated by a reaction with water, and whitening occurs by forming alumina. Thus, the metallic glossiness of the aluminum pigment is impaired. For example, the aluminum pigment formed by coating with a fluorine-based (co)polymer as disclosed in JP-A-2003-213157, JP-A-2006-169393, and JP-A-2009-215411 is not intended to improve waterfastness, and thus, in a case where the aluminum pigment is mixed with an aqueous ink composition, the aluminum pigment is still insufficient from the viewpoint of waterfastness and suppressing the aggregation of the aluminum pigments. In addition, the metal particles disclosed in JP-A-2012-251070 and JP-A-2013-122008 are also not intended to improve waterfastness, and thus, the metal particles are still insufficient from the viewpoint of waterfastness and suppressing the aggregation of the metal particles. From this point of view, an aqueous pigment dispersion which has not only excellent metallic glossiness when mixed with an aqueous coating material or an aqueous ink composition but also excellent dispersion stability (hereinafter, referred to as “water dispersibility”) in the aqueous coating material or the aqueous ink composition has been required.